This invention is generally in the field of digital computer systems and particularly in the field of video and multimedia computer servers.
The National Information Superhighway, a growing web of wide bandwidth communication channels which may soon interconnect most households and businesses in the United States, promises to provide many services to those connected to it. These services may include banking at home, instant access to large databases such as the Library of Congress, and real-time interaction with virtual communities of people with similar interests. Of the services that the Superhighway may make available, one that has received a great deal of corporate and media attention is the provision of video on demand ("VOD").
VOD holds out the promise that almost every movie ever made will be available to a user of the service at any time. Instead of driving to a video rental store and selecting a movie, users will be able to select any movie stored in the system's video library and have that movie delivered to them over the Superhighway.
Before the promise of VOD can be realized, many problems must be solved. Even a relatively short film of two hours duration contains approximately 2.2.times.10.sup.10 bits of data. Standard methods to compress and store the vast quantity of data contained in a film library of thousands of titles must be agreed upon. Even after the data has been captured and stored, there is no agreement on any part of the system that will be needed to deliver the stored data to users.
Any proposed system must satisfy rigorous user demands. Users will want whatever film they have selected delivered to them quickly. They will also want the ability to start and stop the film at any point, as well as the ability to fast forward ("FF") and fast reverse ("FR") the film at will. Provision of these capabilities to every user at any time will place enormous demands on the system's storage units, internal buses, and processing units. Even the enormous bandwidth of fiber optic cable may be exceeded. Additionally, some two-way communication between the user and the system is necessary to communicate users' requests, as well as billing information and the like. This two-way communication places additional burdens on the system.
A fundamental aspect of a VOD video server is the provision of a large amount of data from a data storage system to many users at roughly the same time without significant processing of the outgoing data. What processing capability the system requires is usually relatively simple, such as billing the user's account and archiving the stored video source programs. Envisioning video servers as asymmetrical input/output ("I/O") engines is helpful.
The various system architectures proposed for video servers indicate that the asymmetrical nature of video servers has not been understood. Many proposals suggest the use of mainframe computers to direct and monitor the video data as it flows to the user. In these systems, every request for a film and most system control functions are processed by the mainframe's CPU. Latency time in such an environment can increase dramatically as the number of users increases. Such a use of a mainframe computer is wasteful of the system's processing capability. A video server based on this architecture would be expensive and difficult to expand.
Suggestions which propose the use of networks of personal computers ("PC"s) to provide VOD lack flexibility, as the architecture of PCs was never intended to access and control multiple data storage devices or to control high speed, wide bandwidth output busses.
Although so far discussed only in terms of delivering video data to users, proposed VOD systems will generate data streams which can also include audio, text, graphics and other data types. All references to video data in the specification and claims are intended to include data that comprises either entirely one of these enumerated data types or some mixture of them. Further, nothing herein should be taken to limit the present invention to the storage and transmission of the specifically enumerated data types only.
Before VOD can be realized, a new architecture capable of generating and controlling hundreds, if not thousands of video output streams at relatively low cost must be created. This architecture must be expandable, fault tolerant and capable of efficient operation with video data compressed and stored in any one of several competing formats. No such architecture is presently known.